The commission of selling each iPhone is $30 and the commission of selling each iPad is $20. If you one day sold 4 more iPhones than iPads and earned a total commission of $520, how many iPhones and iPads did you sell respectively?

lets assume number of iphones sold = a number of ipads sold = b i sold 4 iphones more than ipad that becomes a = b+4 then the equation of total commission becomes 30a+20b = 520 substituting a = b+4 in the above equation 30 (b+4) + 20b = 520 30b+120+20b = 520 50b = 520-120 50b = 400 b = 400/50 b=8 number of iphones i sold = a = b+4 = 8+4 = 12 number of ipads i sold = 8 so i sold 12 iphones and 8 ipads to earn the commission of $520